If you use the bottom-left Read Files node (attached to the note that says “Entry point for trimming and PNG-conversion of logos”), the ImageAlpha step makes the logo opaque when it shouldn’t, and badly lowers the saturation of the colors.

If you reconnect the nodes to skip ImageAlpha, the resultant PNG looks fine, and if you drop it into the ImageAlpha app it behaves as expected.

Yes. That bottom path is meant to knock out the corner color, trim to the new edges, reduce palette with ImageAlpha, then write and open in ImageOptim. It does join into the main path’s ImageAlpha node, doesn’t it? That’s where the problem is happening. If none of this makes sense then maybe I uploaded the wrong version of the file… will check later at a computer

No, it seems like I uploaded the right thing. The selected node in this screenshot is the one causing the problem, using the image provided in the node path beginning with “Workflow Notes” there at the bottom left.

My first, completely-uninformed thought was that maybe the Instant Alpha [sic] node isn’t exactly doing an internal conversion from JPEG to a normal PNG the same way it would if you wrote a real PNG file and sent it through pngquant. Let me know if my guess is right!

Alright- I found the bug. It’s fixed now in the latest. RB was basically throwing out the CMYK conversion that was done earlier before handing the pixels off to pngquant. You can grab the new build from here: http://flyingmeat.com/download/latest/#retrobatch